1. Field of the Invention
This invention is in the field of apparatus and process for removing liquid and solid particles from gases, and especially furnace flue gases from coal burning furnaces.
2. Description of the Prior Art
A preferred method for burning coal, in boiler and other furnaces, is as pulverized coal in very small, and hence fast burning particles. The resulting ash particles are much smaller than the already small coal particles, and are, in consequence, difficult tot separate flue gas leaving the furnace. Water spray scrubbers and bag filters are used to remove some of these ash particles from the flue gas, but removal is incomplete. The resulting emissions of ash and other acid particles has limited the extent of utilization of coal, a low cost and readily available fuel.
It would be a public benefit if low cost coal emissions could be made comparable to emissions from more expensive petroleum and natural gas fuels. Known reserves of coal, both nationally and worldwide, are much greater than known reserves of petroleum and natural gas.
3. Definitions
The following terms are used herein and in the claims as defined herewith:
An expander is a gas flow channel through which gas flows from a higher pressure to a lower pressure. Some expanders, such as gas or steam turbines, are expander engines which produce a network output. The expander pressure ratio is the ratio of expander inlet pressure divided by expander outlet pressure.
Water can mean a liquid or a vapor or a mixture of both as in wet steam.
Flue gas is any industrial gas, such as the exit gas from a pulverized coal fired furnace. Many flue gases contain particles and other components, such as acids, which are preferably removed from the flue gas before discharge into the atmosphere.
A separator is a gas flow channel, within which a force is applied to the gas, such as centrifugal force or electrostatic force, generally across the principal direction of flow, tending to separate higher density materials from lower density materials.
A flue gas cleaner of this invention adds water vapor to a furnace flue gas and then expands the gas through a sufficient pressure decrease that water vapor condensation can occur. Particles in the flue gas and acid molecules trigger the water vapor condensation upon themselves, thus rendering them more readily separable from the flue gas. The expanded flue gas is passed through one or more separators, such as centrifugal separators or electrostatic separators, in order to separate the wetted particles and acids from the flue gas. The thusly cleaned flue gas is then compressed back up to chimney or other discharge pressure. The collected condensate is pumped out of the separator into a condensate collector.
It is a principal beneficial object of this flue gas cleaner invention, that very small particles, such as those formed in pulverized coal fired furnaces, can be wetted, and their mass increased, rendering them more easily separable from the furnace flue gas. In this way, low cost coal fuel can become more widely used while meeting appropriate emissions requirements.